Induction motor driven seal-less pump

ABSTRACT

A seal-less pump and electric motor assembly includes a motor rotor fixed to a driving shaft connected to an impeller in the pump assembly. The rotor and impeller are enclosed in a common housing such that the rotor rotates within any fluid being pumped by the impeller. The portion of the housing circumscribing the rotor includes a plurality of axially extending, circumferentially spaced strips of magnetic material penetrating through plastic material of the housing. Each of the strips coincide with corresponding ones of the pole teeth of a motor stator circumscribing the outer portion of the housing such that the strips in the housing act as extensions of the pole teeth. In one embodiment, the strips of magnetic material in the housing are formed by molding powdered iron in a plastic binder material. The strips are then placed in a mold in which the housing is formed by injecting plastic. The plastic binder in the strips melds with the injected plastic to form a continuous housing for enclosing the rotor. The ferromagnetic material strips extend through the housing and are spaced from the rotor surface by a normal air gap distance so as to improve the efficiency of the motor by having the magnetic strip act as extensions of the motor stator pole teeth. In one embodiment, the rotor includes a shaft, a core-including a molded magnetic powder and plastic composite material surrounding the shaft, and an annular corrosion resistant electrically conductive tube surrounding the core.

BACKGROUND OF THE INVENTION

[0001] This invention relates to electric motor driven fluid handlingassemblies and, more particularly, to a seal-less pump and motorassembly having improved electrical characteristics.

[0002] There are various applications in which a mechanical apparatusmay be exposed or immersed in a fluid and adapted for being driven by anelectric motor. Typical examples are a water pump in a dishwasher orclothes washing machine and an agitator in a clothes washing machine. Insuch applications, it is desirable to isolate the electric motor fromthe water both to protect the motor and to prevent electric shockhazards. A classic method of isolating the electric motor is to extend ashaft from the mechanical apparatus through a seal to the motor. Theshaft to seal interface must provide for relative shaft motion andtherefore is subject to wear and deterioration leading to fluid leaks atthe interface.

[0003] An alternative strategy which avoids the potential seal leakageis to place the motor into the fluid environment. However, this strategyis inadvisable for water pumps and can be expensive when the electricalconnections of the motor must be fluid proof.

[0004] Another method which avoids the seal leakage problem is toconstruct the apparatus, e.g., a pump, within a housing which alsoencompasses the motor rotor. The housing closely envelopes thecircumference of the rotor without contact. The motor stator is thenpositioned outside the housing about the rotor. With a typical plastichousing, this arrangement requires a relatively large space between therotor and stator, i.e., the effective “air gap” may be as much as 10times the normal motor gap for an induction motor. For example, aminimum thickness for a plastic housing is generally about 0.09 incheswhile a nominal air gap for an efficient induction motor is about 0.01inch. The resulting construction produces a motor which is oversized,expensive and inefficient with poor operating characteristics.

[0005] Still another prior art attempt to resolve the electricmotor/pump problem of isolating the motor from the pumped fluid is touse a permanent magnet motor. Such a motor is expensive due to both themagnet cost and fabrication costs to meet water resistant constraints.Further, simple single phase permanent magnet synchronous motors aresometimes used for this purpose and are difficult to start in acontrolled direction and have synchronization problems. If anelectronically commutated control is used, the motor and drive costincreases dramatically.

[0006] Another challenge when designing a seal-less pump is that, evenin relatively clean water, the wet rotor of a seal-less pump is subjectto corrosion because of the presence of dissolved oxygen. A conventionaltechnique for resisting corrosion is to coat the rotor with a materialsuch as a plastic or an epoxy or to plate the rotor with a corrosionresistant metal such as aluminum. Crevices between rotor laminationsand/or between rotor laminations and the rotor cage cause effectivesealing to be difficult, and the coatings sometimes fail after a numberof immersions.

[0007] To avoid the crevices, a solid iron rotor can be used. Sheetrotors comprising a copper shell brazed to a solid steel core are usedin X-ray tube target rotators to withstand high temperatures, highspeed, and vacuum conditions. Such rotors are typically coated withinfra-red emitters.

[0008] Solid iron and steel cores can become corroded, and skin effectscan affect electromagnetic steady state performance in the solid coreseven at low slip frequencies. These skin effects can lead todifficulties in starting the rotor.

SUMMARY OF THE INVENTION

[0009] Among the several objects of the present invention may be notedthe provision of an induction motor driven fluid handling apparatuswhich eliminates the necessity of a seal at any rotating interface; theprovision of an induction motor driven fluid handling apparatus in whichthe motor rotor is encompassed by an apparatus housing while the motorair gap is maintained at a nominal value; the provision of an inductionmotor driven fluid handling apparatus which overcomes the size,inefficiency and poor operating characteristics of prior seal-lessmotors; the provision of a method for construction of an induction motordriven seal-less pump; and the provision of an economical method ofmaking a corrosion resistant induction motor rotor that will have a goodelectromagnetic performance.

[0010] Briefly, in one embodiment a seal-less pump and electric motorassembly includes a motor rotor fixed to a driving shaft connected to animpeller in the pump assembly. The motor rotor and impeller are enclosedin a common housing such that the rotor rotates within any fluid beingpumped by the impeller. The portion of the housing circumscribing themotor rotor includes a plurality of axially extending, circumferentiallyspaced strips of magnetic material penetrating through the insulativeplastic material of the housing. Each of the strips coincide withcorresponding ones of the pole teeth of a motor stator circumscribingthe outer portion of the housing such that the strips in the housing actas extensions of the pole teeth.

[0011] In another embodiment, a rotor of a seal-less pump comprises arotor shaft, a rotor core including a molded magnetic powder and plasticcomposite material surrounding the rotor shaft, and an annular corrosionresistant electrically conductive tube surrounding the rotor core.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding of the present invention, referencemay be had to the following detailed description taken in conjunctionwith the accompanying drawings in which:

[0013]FIG. 1 is a simplified cross-sectional view of a prior artseal-less pump and electric motor assembly;

[0014]FIG. 2 is a simplified cross-sectional view of a seal-lesspump/induction motor assembly incorporating the present invention;

[0015]FIG. 3 is a perspective view of a pump enclosure segment accordingto the present invention;

[0016]FIGS. 4 and 5 are enlarged sectional views of sections of theenclosure segment of FIG. 3 showing alternate forms of magnetic stripsand pole teeth extensions.

[0017]FIGS. 6, 6A, 6B, 6C, 6D, and 6E illustrate still othercross-sectional shapes for the magnetic strips and pole teethextensions;

[0018]FIGS. 7 and 8 illustrate manufacturing steps for producing theinventive housing segment;

[0019]FIG. 9 is a view of a conventional rotor lamination sheet;

[0020]FIG. 10 is a perspective view of a rotor embodiment of the presentinvention; and

[0021]FIGS. 11 and 12 are sectional side views of a fixture forfabricating the rotor of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

[0022]FIG. 1 is a simplified cross-sectional view of a prior artseal-less pump/induction motor assembly of the type with which thepresent invention may be used. The pump 10 comprises an impeller 12positioned in an enclosure 14 forming a portion of a pump housing 16.Another enclosure 18 forms another portion of housing 16 and encompassesa rotor 20 of an alternating current (AC) induction motor 22. Thehousing 16 is circular about an axis 24 through the motor rotor 20 andimpeller 12. A shaft 26 of rotor 20 lies on axis 24 and connects toimpeller 12 so that rotation of rotor 20 drives impeller 12. An O-ring28 positioned in an annular groove 30 in a wall 32 of enclosure 14provides a watertight seal between enclosure 14 and enclosure 18.Enclosure 18 may be attached to enclosure 14 by threaded fasteners,clamps or other means well known in the art. For simplicity, neither theenclosure-to-enclosure attachment means nor the pump inlet and outletlines are shown. Further, the bearing assemblies which support shaft 26for rotation are omitted.

[0023] The motor 22 includes a stator 34 positioned outside enclosure 18circumscribing rotor 20. Pole faces of stator 34 are desirably abuttingthe outer surface of enclosure 18 in order to reduce the gap between thepole faces and the outer surface of rotor 20. However, the minimumthickness of enclosure 18 is limited to about {fraction (3/32)} inch inorder to provide sufficient strength and stiffness of the enclosure. Forgood performance and efficiency and reasonable size, the desired airgap, i.e., the spacing between the stator pole teeth faces and the rotorouter surface should be about {fraction (1/100)} inch. Thus, the plasticenclosure 18 results in a stator-rotor gap which is about 10 times thedesired gap and detrimentally affects motor size, performance andefficiency. Obviously, the stator 34 operates in open air while rotor 20is submerged in whatever fluid, e.g., water, is being pumped.

[0024] Turning to FIG. 2, there is shown a cross-sectional view takenalong the line 2-2 of FIG. 1, illustrating an improved electric motordriven pump assembly in accordance with the present invention. Theelements of FIG. 1 remain unchanged, the invention lying in theconstruction of enclosure 18. Considering FIG. 2 in combination withFIG. 3, it will be seen that the inventive enclosure 18 is constructedwith a plurality of circumferentially spaced ferromagnetic strips 36integrally formed in the plastic material of enclosure 18, i.e., thestrips 36 alternate with plastic elements 48. Each of the strips 36 hasan inner face 38 coincident with the inner face 40 of enclosure 18allowing the strips 36 to be closely positioned facing rotor 20,preferably within {fraction (1/100)} inch. The strips 36 extend throughenclosure 18 and are accessible from an outer surface of enclosure 18allowing direct contact with respective pole teeth members 42 of stator34. For simplicity, the windings 44 of FIG. 1 are not shown in the poleteeth interstices 46 of FIG. 2. It will be appreciated that variousnumbers of pole teeth may be used and that there may be multiple poleteeth in each magnetic pole of stator 34. The strips 36 are desirablyformed with the same axial length and width as the pole teeth 42.

[0025] As shown in FIG. 3, at least a portion of the enclosure 18 may beformed as an annular sleeve comprising a plurality of molded magnetictooth tips or strips 36 interspersed with conventional plastic strips 48to form a segmented ring 50. In general, the strips 36 are formed bycombining iron powder in a plastic matrix and then either extruding ormolding the individual strips 36 from the plastic into a shape to matchthe width and length of a stator tooth with which the ring is to beused. Once the strips 36 have been formed, these strips can then be setinto a die or mold that will be used to make the injection molded pumpshell or enclosure 18 and molded in place with the remainder of theenclosure 18. The sizing of the segmented ring 50 is selected so thatwhen the motor stator is slid over the enclosure 18, there is a tightfit between each of the strips 36 and a corresponding one of the poletooth members 42. In effect, the strips 36 become extensions of the poleteeth 42. In this way, the magnetic gap is reduced to that of only thespacing between the outer surface of the rotor 20 and the inner surfaceof the enclosure 18. Such spacing may be only that gap required toprovide a mechanical clearance between the enclosure 18 plus a few milsfor stator fit mismatch. Thus, the motor 22 may be of conventionaldesign and size except for a small extra tooth leakage flux and aslightly larger effective gap between the ends of the stator teeth andthe outer surface of the rotor 20. It is expected that the powdered ironin the plastic or epoxy matrix will have a lower permeability and higherlosses than a steel lamination, but since the volume of the powderediron matrix is relatively small, the effect will not be of majorsignificance in overall motor performance. A typical powdered ironmaterial useful in forming the strips 36 of the present invention isavailable from the Hoeganaes Corporation in the form of an atomized ironpowder, similar to that used in sintered powder metallurgy production,but with each particle of iron powder coated with a layer of ULTEM™polyetherimide (ULTEM is a registered trademark of the General ElectricCompany).

[0026] Referring now to FIGS. 4 and 5, there is shown enlargedcross-sectional views of a portion of the enclosure 18 with twodifferent forms of the strips 36. In both FIGS. 4 and 5, the enclosure18 is molded with the strips 36 having a different radial thickness thanthe adjacent plastic sections between the strips. Accordingly, theenclosure 18 appears to have a plurality of grooves 52 overlying each ofthe strips 36. The grooves facilitate accurate matching of the stator tothe magnetic strips by forcing the stator teeth into the grooves betweenthe plastic elements and onto the ferromagnetic strips 36. During theassembly process, the grooves enable the stator to be guided into theproper position without any special tooling. For conventional motorstators having a broad or widened tooth tip 54, the arrangement shown inFIG. 4 may be preferred in which the broadened tooth tips simply matewith a wide strip 36. The strips 36 then merely create an extra thicktooth tip. This arrangement results in some additional leakage flux witha penalty in the pullout torque generated by the motor but stillprovides significant advantages over the prior art. An alternative is tofabricate the stator teeth with straight segments as shown in FIG. 5 andto form the strips 36 in a conventional tooth tip configuration. Thisarrangement improves the leakage flux problem and further improvespullout torque but does require a redesign of the stator laminations toproduce the stator teeth without the conventional tooth tip 54.

[0027] It will also be noted in FIG. 4 that the strips 36 are formedwith grooves 56 along opposite sides. These grooves 56 may be useful inproviding a better binding of the strips 36 to the adjacent plasticsections 48 of the enclosure 18. FIG. 6 illustrates some additionalshapes which may be useful in forming the strips 36. These additionalshapes may be useful in providing improved sealing, simplifyingmanufacturing or merely to give greater strength to the outer shell ofenclosure 18.

[0028]FIGS. 6A, 6B, 6C, 6D, and 6E illustrate other shapes of the poleteeth extensions and strips 36. The radial shape of a magnetic stripaffects the flux pattern in the magnetic strip and can provide variousphysical features to enhance the fabrication process. The shape of astrip can be used to aid the flux transition from a high permeabilitysteel to a lower permeability magnetic strip and to reduce volumeoccupied by a magnetic strip. Cost of a magnetic strip is proportionalto density. It can be cost effective therefore to reduce the density ofa magnetic strip while permitting an acceptable level of magneticlosses. The required magnetic strip density can be decreased by reducingthe flux density and total flux passing through the magnetic strip.

[0029]FIG. 6A encourages alignment of the stator pole teeth members 42with strips 36 by forming each strip 36 with a radially outwardextending portion 36A. Pole teeth members 42, preferably formed ofpunched and stacked laminations, are designed with an end shaped with adepression to fit about and abut against strips 36. The height of theportion 36A above the outer surface of the rotor shell 48 is about 0.057inches for a sleeve or shell 48 thickness of about 0.081 inches. Thisembodiment is useful for alignment but requires more magnetic stripmaterial and promotes a higher flux density in the transition region.

[0030]FIG. 6B is a reversal of FIG. 6A in which the pole teeth members42 are formed with a rounded protuberance 42A which fits into andengages a shaped depression 36B in strip 36. This embodiment aidsalignment, reduces the amount of strip material required, and promotes alower flux density in the transition region of the magnetic strip.

[0031] Two potential challenges to fabrication of the seal-less pump areinterference of stator winding endturn bundles (not shown) withsegmented ring 50 (and pump/rotor housing 18) and difficulty in holdingthe stator windings in the stator slots prior to assembly with thepump/rotor housing.

[0032]FIG. 6C is a view of a stator tooth having vestigial tips 37 whichprotrude into the stator slot to help hold in place any slot insulatorand/or slot wedge. Depending upon the size of the vestigials, thevestigials can also be useful for holding the slot windings in position.Having depressions in strip 36 and protuberances in teeth member 42, asshown in FIGS. 6B-6E, provides an increase in the minimum diameters thatthe endturn bundles can occupy towards the bore.

[0033]FIGS. 6D and 6E illustrate alternative positions for the vestigialtips where the edges of the vestigial tips are not aligned with themagnetic strip. In FIG. 6D, vestigial tips 37 a are wider than themagnetic strip edge, and in FIG. 6E, vestigial tips 37 b are narrowerthan the magnetic strip edge.

[0034]FIGS. 7 and 8 illustrate other possible intermediate stages offabrication of an enclosure 18 in accordance with the present invention.In FIG. 7, the magnetic portion of a segmented ring 58 is positioned ona mandrel 60. The segmented ring 58 comprises a plurality of powderediron and plastic composite tooth tips or strips 36 which can be bondedtogether by plastic strips 48 molded in between as shown in FIG. 3. Thesegmented ring 58 is initially formed on the mandrel 60 in a compressionmolding operation as shown in FIG. 8. A small end ring 62 of material isleft at one end to assure that the teeth 36 remain in proper alignment.The mandrel 60 is coated with a release compound and has an outerdiameter which forms the inner diameter of the segmented ring 58, i.e.,it has a diameter equal to the diameter of the motor rotor 20 plus adesired clearance gap, e.g., about {fraction (1/100)} inch. The mandrel60 is positioned into a die 64 which has a plurality of slotssurrounding the mandrel with each of the slots having the desired lengthand configuration of a strip 36 to be molded. The powdered iron andplastic matrix, e.g., ULTEM™ polyetherimide, is poured into the die 64to fill the space around the mandrel 60 and a ram 66 is then broughtdown into the die 64 to compression form the segmented ring. The die 64is heated during compression to mold the powdered iron and plastic intoa composite part.

[0035] After molding, the mandrel 60 with the molded tooth tips orstrips 36 attached is then withdrawn from the die 64. The mandrel 60 andtooth tips 36 are then inserted in a second die (not shown). A moltenplastic is then injected into the spaces between each of the preformedstrips 36 while the strips are in the die so that the spaces betweeneach of the strips is filled with the molten plastic. The temperatureand pressure with which the plastic is injected is selected based uponnormal production injection molding of parts. The injected plastic willbond with the plastic base of the magnetic strips 36 thus forming awatertight solid enclosure. Preferably, the plastic is filled with glassfiber such that the expansion coefficients of the tooth tips 36 and theintermediate filler are reasonably matched. After molding and removalfrom the die, the temporary end ring 62 which was used to hold themolded strips 36 together can be severed from the final segmented ring.The enclosure 18 is then completed by positioning the segmented ring 50(See FIG. 3) into a conventional pump casing mold (not shown) whichmolds the final entire enclosure 18 in a conventional manner.

[0036] While the above described method of producing the segmented ring50 is a preferred method, an alternate method may be to extrude the ring50 as a composite ring with both the magnetic strips 36 and theintermediate plastic sections in a single operation. Since the plasticbase used in both the strips and the bonding plastic are the same orcompatible, they will merge and bond in the process. The tooth tipsformed by the extrusion process will be less dense than those formedusing the compression molding process and will result in somewhat poorerelectromagnetic performance. However, since the tooth tips form a verysmall part of the total magnetic circuit, it is believed that there willbe little difference in overall motor performance between extruded andcompression molded tooth tips.

[0037]FIG. 9 is a view of a conventional rotor lamination sheet 110.Induction motor rotors for small machines are conventionally fabricatedby punching thin steel sheets (having thickness ranging from about 0.018inches to about 0.030 inches) and stacking the sheets to form the rotorcore. The holes near the periphery of the rotor core are generallyfilled with molten aluminum to form the rotor windings. Rings ofaluminum are molded onto the ends of the windings to connect thewindings together and form a “squirrel cage” winding. Stacking of rotorcore sheets (laminations) permits the magnetic flux to fully penetratethe rotor during starting, aides in torque production, and can increaseefficiency of the rotor during operation. Rotor stacks are often skewedto minimize slot interaction effects. As discussed in the backgroundabove, conventional induction motor rotors are conducive to corrosionwhen they become wet.

[0038] Starting and running performance of a corrosion resistant rotorcan be achieved by pressing or shrink fitting an annulus of electricallyconductive, corrosion resistant material over a solid steel rotor core.For solid steel rotor cores, there will be skin effects, especiallyduring starting, and corrosion occurs.

[0039]FIG. 10 is a perspective view of a rotor embodiment of the presentinvention. A rotor core 112 comprises a molded magnetic powder/plasticcomposite material. In one embodiment, irregularly shaped iron particlesindividually coated with a plastic material such as ULTEM™polyetherimide are compression molded with a shaft hole. Other examplesof appropriate magnetic materials include steel, ferrite (iron oxide),stainless steel, nickel, and cobalt. Other examples of appropriateplastic materials include polymers and epoxies. The rotor fabricationprocess then is completed by applying a shaft 114 comprising a corrosionresistant material such as stainless steel and an annular tube 116comprising a corrosion resistant electrically conductive material suchas aluminum, brass, or copper. In another embodiment, the core isfabricated by extruding a long rod of material with a central hole andcutting off suitable lengths. This less expensive fabrication processresults in some surface corrosion from metal exposed by cutting the endsurfaces.

[0040]FIGS. 11 and 12 are sectional side views of one embodiment of afixture 118 for fabricating the rotor of FIG. 10. First, hollow aluminumtube 116 is baked in air to form a hard aluminum oxide coating on allsurfaces to resist corrosion. Tube 116 is positioned in a cylindricaldie fixture 118. Shaft 114 is also positioned in the fixture. Thefixture, tube, and shaft are then preheated to a predetermined moldingtemperature, and the coated iron particles 129 are preheated and pouredinto the fixture. It is useful to have a mold piece 120 adjacent tube116 and fixture 118 to better guide particles 112 a between the tube andthe shaft and to prevent distortion of the tube 116. It is also usefulto have a notch 124 in fixture 118 for supporting the rotor shaft.

[0041] The poured volume of particles should be greater than thefinished rotor core size to allow for compression. A ram 122 can bebrought down with a suitable force to compress the volume of particles,and raising the temperature will cause the particles to bond togetherand form a solid mass 112. After a cooling period, the finished rotorcan be removed from the die. Whether preheating and/or cooling isnecessary is dependent on the plastic material coating the ironparticles.

[0042] The rotor of the present invention is expected to have good fluxpenetration and low losses in running. The molding process will leave afilm of bonding material on the surface of the rotor which will providean additional barrier to the individual particle coats, and a close bondbetween the core and the tube will prevent the entry of moisture intothe core.

[0043] While the invention has been described in what is presentlyconsidered to be a preferred embodiment, many variations andmodifications will become apparent to those skilled in the art.Accordingly, it is intended that the invention not be limited to thespecific illustrative embodiment but be interpreted within the fullspirit and scope of the appended claims.

What is claimed is:
 1. An electric motor and pump assembly comprising: apump assembly including an impeller and having a driving shaft extendingfrom the impeller; a motor rotor fixed to the driving shaft; a pumphousing extending around the motor rotor and the impeller; a motorstator circumscribing the motor rotor outwardly of the housing, thestator having a plurality of radially inwardly extending magnetic poleteeth sized and arranged to engage an outer surface of the housingapproximately co-extensively with an axial dimension of the motor rotor;and said housing being formed with a plurality of axially extending,circumferentially spaced strips of magnetic material, each of saidstrips being aligned with and engaging a corresponding one of the poleteeth for forming pole teeth extensions in said housing closely spacedto said rotor.
 2. The assembly of claim 1 wherein said housing comprisesa molded plastic segment encompassing said motor rotor, said stripsbeing integrally molded into said segment.
 3. The assembly of claim 2wherein each of said strips of magnetic material are recessed below anouter surface of adjacent portions of said plastic segment.
 4. Theassembly of claim 2 wherein each of said strips of magnetic materialincludes a radially outward extending portion and each of said poleteeth includes an end with a depression shaped to fit about a respectiveoutward extending portion.
 5. The assembly of claim 2 wherein each ofsaid pole teeth includes a radially outward extending portion and eachof said strips of magnetic material includes an end with a depressionshaped to fit about a respective outward extending portion.
 6. Theassembly of claim 5 wherein each of said pole teeth includes vestigialtips.
 7. The assembly of claim 2 wherein each of said pole teethincludes vestigial tips.
 8. The assembly of claim 2 wherein said stripsof magnetic material comprise molded strips of powdered iron in aplastic binder material.
 9. The assembly of claim 2 wherein each of saidstrips of magnetic material is shaped in the form of a conventionalstator tooth tip.
 10. An electric motor driven pump assembly in whichthe pump includes an impeller coupled directly to a rotor of the motorwith the rotor and impeller exposed to a fluid and the motor statorbeing isolated from the fluid by a plastic pump housing segmentcircumscribing the motor rotor, the stator being characterized by aplurality of radially inward extending pole teeth electrically andmechanically engaging corresponding ones of a plurality of strips ofelectrically conductive material formed by combining powdered iron in aplastic matrix, the strips being embedded in the plastic pump housingsegment.
 11. A method of fabricating a component of a motor-pumpcombination comprising the steps of: molding a powdered ferromagneticmaterial into an end ring having a plurality of strips of the powderedferromagnetic material depending generally axially from the end ring andpredeterminately spaced apart circumferentially about the end ring;injecting a resin material strip in bonding relation between adjacentpowdered ferromagnetic material strips on the ring and forming agenerally annular sleeve extending from the end ring with the annularsleeve, comprising the resin material strips bonded between the powderedferromagnetic material strips in response to the injecting step; andsevering the end ring from the annular sleeve.
 12. The method as setforth in claim 11 wherein the injecting step includes establishing apair of opposed guide faces along each adjacent resin material stripwith the opposed guide faces extending axially across the outercircumference of the annular sleeve.
 13. The method as set forth inclaim 11 wherein the injecting step includes establishing a plurality ofguide slots generally axially across the outer circumference of theannular sleeve with adjacent resin material strips defining opposedsidewalls in each guide slot and one of the powdered ferromagneticstrips between the adjacent resin material strips defining a base wallof each guide slot interposed between the opposed sidewall thereof. 14.A method of fabricating a motor-pump combination with the motor thereofhaving a stator, the stator including a pair of generally opposite endfaces, a plurality of teeth extending between the opposite end faces,and a plurality of tooth tips on the teeth defining in part a generallyaxial bore between the opposite end faces, respectively, the methodcomprising the steps of: forming a generally annular sleeve and bondinga resin material strip of a set of resin material strips inpredetermined spacing actuation, between adjacent ferromagnetic stripsof a set of ferromagnetic strips during the forming step with the stripsextending generally axially in the annular sleeve; molding a resinmaterial casing member for the pump of the motor pump combination withthe casing member having a generally annular cylindric section andincluding the annular sleeve in part in the annular cylindric sectionduring the molding step; and inserting the annular cylindric sectioninto the bore of the stator and aligning the ferromagnetic strips of theannular sleeve in abutting engagement with the tooth tips on the teethof the stator upon the assurance of the inserting step.
 15. The methodas set forth in claim 11 wherein the bonding step includes establishinga pair of opposed guides on each adjacent resin material strip duringthe bonding step.
 16. The method as set forth in claim 15 wherein theinserting step includes receiving the teeth of the stator in guidingrelation between the opposed guides on the annular sleeve, respectively.17. The method as set forth in claim 14 wherein the bonding stepincludes establishing a plurality of guide slots generally axiallyacross the outer circumference of the annular sleeve with adjacent resinmaterial strips defining opposed sidewalls of each slot and one of theferromagnetic material strips between the adjacent resin material stripsdefining a base wall of each guide slot between the opposed sidewallsthereof.
 18. The method as set forth in claim 17 wherein the insertingstep includes sliding the teeth of the stator into the guide slots inthe annular sleeve in guiding relation with the opposed sidewalls of theguide slots, respectively.
 19. The method as set forth in claim 18wherein the sliding step includes abutting the tooth tips with the basewall of the guide slots respectively defined by the ferromagneticmaterial strips in the annular sleeve.
 20. A rotor for use in aseal-less pump and electric motor assembly, the rotor comprising: arotor shaft; a rotor core including a molded magnetic powder and plasticcomposite material surrounding the rotor shaft; and an annular corrosionresistant electrically conductive tube surrounding the rotor core. 21.The rotor of claim 20 wherein the magnetic powder and plastic compositematerial includes iron particles coated by polyetherimide.
 22. The rotorof claim 20 wherein the electrically conductive tube includes analuminum coated by aluminum oxide.
 23. A method of fabricating a rotorcomprising the steps of: molding a magnetic powder and plastic compositematerial to form a rotor core having a shaft hole; providing a shaft inthe shaft hole; and providing an annular corrosion resistantelectrically conductive tube around the rotor core.
 24. The method ofclaim 23 wherein the step of molding comprises inserting theelectrically conductive tube and the shaft into a molding fixture,pouring plastic coated iron powder into the molding fixture, andcompressing the plastic coated iron powder.
 25. The method of claim 24further including preheating the electrically conductive tube, theshaft, the fixture, and the plastic coated iron powder prior to pouringthe plastic coated iron powder.
 26. The method of claim 25 wherein thestep of compressing the plastic coated iron powder includes raising thetemperature of the plastic coated iron powder and using a ram to applysuitable force to the plastic coated iron powder.
 27. The method ofclaim 23 , further including, prior to providing the electricallyconductive tube around the rotor core, oxidizing the electricallyconductive tube.